(a) Field of the Invention
The present invention generally relates to a synchronization method and apparatus for a device-to-device direct communication.
(b) Description of the Related Art
Conventional wireless communication systems use a master-slave synchronization scheme. In the master-slave synchronization scheme, one device becomes a master and transmits a reference signal, and the other devices adjust reference times based on the reference signal transmitted by the master. In a cellular system, a base station always operates as the master. However, because a direct communication between terminals can be performed under a circumstance where the base station does not exist, the master-slave synchronization scheme is not suitable for the cellular system.
In an ad-hoc network where there is no base station for operating as the master, the terminal senses carriers using a carrier sense multiple access (CSMA) scheme, and performs back-off during a predetermined time. After a timer expires, the terminal becomes the master and transmits a reference signal. In this case, consumption of resources for performing the back-off is inevitable. Furthermore, a terminal between the two master terminals may simultaneously receive two reference signals having the different synchronizations. Then, the terminal may encounter near-far problem increasing the interference.